The present invention relates generally to plasma cutting systems and, more particularly, to a method and apparatus for coordinating operational feedback in a plasma cutter. Specifically, the present invention provides a system and method of serializing feedback from a plasma-cutting torch to a plasma-cutting power source.
Plasma cutting is a process in which an electric arc is used to cut a workpiece. Plasma cutters typically include a power source, an air supply, and a torch. The torch or plasma torch is used to create and maintain the arc and plasma that perform the cutting. The plasma cutting power source receives an input voltage from a transmission power line or generator and provides an output voltage to a pair of output terminals, one of which is connected to an electrode and the other of which is connected to the workpiece.
The air supply is used with most plasma cutters to help start the arc, provide the plasma gas to the torch, and cool the torch. A movable or fixed electrode serves as a cathode and a fixed nozzle serves an anode. The air supply moves the electrode and as the electrode moves away from the nozzle, it opens the nozzle, and a plasma jet is created. The plasma jet causes the arc to transfer to the work piece, and thus initiates the cutting process. In other plasma cutting systems, a high frequency starter is used to initiate the cutting process.
The power source is supplied with operational feedback from the torch and a processor, disposed in the power source, interprets the data and controls the operation of the plasma cutter. For example, the processor of the power source is provided with feedback about the position of the torch trigger and whether all necessary torch components are securely in place at the torch. From the feedback, the processor determines whether to initiate cutting, pause cutting, discontinue cutting, or augment the operation of the plasma cutter during cutting.
This feedback is typically provided via dedicated communications lines. Therefore, for each form of feedback that is sent from the torch to the power source, an individual communications line is connected between the power supply and cutting torch. This parallel feedback system presents numerous drawbacks.
First, plasma cutting is a high voltage process and therefore the user must be mindful that precautionary measures must be taken to avoid improper operation. As such, it is necessary to determine whether specific conditions are present prior to the initiation of cutting. For example, before the power source responds to a request for operational power at the torch, the processor of the power source typically determines whether a retaining cup, fastened at the torch tip and securing the electrode, is in place. This ensures that the torch is in operating condition prior to cutting. However, while it is common to provide a cup-attached signal before permitting operational cutting, the number of feedbacks is limited by the parallel feedback system. Specifically, since the feedback must be sent from the torch to the power source, the feedback must travel over a control cord connecting the torch and power source. To control manufacturing costs and maintain portability of the plasma cutter, it is necessary to limit the number of parallel communications links between the torch and the power source. As such, though additional sensors could be included to provide additional feedback regarding the plasma cutting process, the number of sensors to provide feedback is limited by the number of parallel communications links.
Second, plasma cutters are regularly subjected to harsh operating conditions associated with the operating environment in which they are placed and the nature of plasma cutting. For example, plasma cutters are commonly operated within large manufacturing environments or at an in-field site. As a result of these typically callous operating environments, it is possible for one of the communications lines to fail as a result of repeated percussions. Furthermore, it is not uncommon for the plasma torch to be regularly disconnected from the power source for cleaning and maintenance. This repeated disconnection and reconnection can be particularly damaging to the electrical connections of the parallel feedback system. In either case, if the parallel feedback system fails, the plasma cutter must be removed from service and repaired or otherwise serviced.
It would therefore be desirable to design a plasma cutting system that is capable of providing multiple feedback signals to the power source. Specifically, it would be desirable to design a plasma cutting system having a more robust feedback communications system.